This invention relates to a spark-ignited reciprocating-piston internal combustion engine with a combustion chamber subdivided in the top dead center zone (with piston in top dead center position) into two chambers, between which a cross connection exists in the region of the piston rim, one of these chambers being associated with the source of ignition and forming a combustion duct between the source of ignition and the cross connection.
In a conventional construction of this type, such a design with two chambers is to prevent the efflux of uncombusted gases in the overlapping range of the opening times of inlet and outlet elements and, simultaneously, combustion dead times are also to be avoided. In summation, these measures are to serve for reducing the content of pollutants in the exhaust gases of such internal combustion engines (DOS [German Unexamined Laid-Open Application] No. 2,455,960).
In contrast thereto, the invention is based on the object of affecting the heating principle, i.e. the combustion characteristic, of such internal combustion engines so that a low proportion of nitrogen oxides is obtained and, by accelerating the combustion, a low specific fuel consumption is achieved.
According to the invention, this can be accomplished in a spark-ignited reciprocating-piston internal combustion engine of the aforementioned type by providing that the ignition takes place only after separation of the compression volume into the two chambers (ignition only after piston and cylinder are in relative positions forming two chambers).
To separate the compression volume into the two chambers, it is contemplated within the scope of this invention to provide mutually opposed bridges or lands on the piston and cylinder sides, which lands overlap in the dead center zone with the formation of a gap therebetween.
According to another preferred embodiment of this invention, for separating the two chambers, a combustion duct is associated with the cylinder, which duct adjoins the piston periphery so that it can be passed over by the piston, i.e. it can essentially also be segregated from the second chamber.
The separation of the two chambers prior to ignition and the formation of a combustion duct by means of one of these chambers offers the possibility, as has been demonstrated by experiments, of affecting the combustion rate in the direction toward a desired combustion characteristic, namely by fashioning the cross-sectional extension of the combustion duct from the spark plug vertically to the direction of movement of the flame front approximately in proportion to the predetermined combustion characteristic, wherein a reduction in the cross section results in an increase in the combustion rate. This possibility of influencing the combustion characteristic forms the prerequisite for being able to operate at a high compression .epsilon. without the occurrence of spontaneous ignitions, since the maximum pressure p.sub.max in the combustion chamber can be correspondingly controlled by the aforementioned design of the cross section. Thus, no spontaneous ignitions of unconsumed mixture proportions take place during the progression of the combustion. The high compression ratio .epsilon. also leads to a low fuel consumption, and the limitation of the peak pressure reduces the combustion noise, so that, as seen in total, spontaneous ignitions can be avoided in spite of a high compression and a smooth combustion process can be achieved.
The influence on the peak pressure and the possibility of limiting same also provides the capability of lowering the temperatures so that the formation of nitrogen oxides is extensively avoided.
On the other hand, the possibility of operating at a high compression ratio while yet maintaining the aforementioned advantages leads to the feature that a relatively lean mixture can be utilized without the danger of ignition failures or misfirings, whereby the proportion of carbon monoxide in the exhaust gases can be reduced.
Finally, the deflection or guidance of the combustion process also has the effect that the flame front as such remains preserved for a longer period of time than in conventional internal combustion engines, whereby also those mixture proportions are utilized which exit from the gap spaces upon a pressure drop and whereby the proportion of hydrocarbons in the exhaust gases can be maintained at a minor value.
Above and beyond the above-mentioned advantages, the solution of this invention of subdividing the system into two combustion chambers also offers the advantage that a layering of the mixed charge can be attained in a simple manner without having to provide a separate chamber, so that the disadvantages occurring in conventional engines operating with separate chambers and a layered charge--namely a lack in the flushing of the chamber--are avoided.
A particularly simple construction, which additionally provides a layering feature in an advantageous manner, can be obtained especially in those embodiments wherein the combustion chamber, in association with the cylinder, is arranged adjoining to the piston circumference and can be passed over by the piston. In this connection, the combustion duct is preferably disposed in the transition between the cylinder head and the cylinder block. The combustion duct is preferably arranged so that it is first of all passed through by the mixture exiting from the inlet valve. The fuel particles then are deposited in the sack-like combustion duct and thereby enrich the mixture in the spark plug zone.
The combustion duct can also be disposed in the cylinder skirt according to other preferred embodiments, and in those solutions wherein the combustion duct is associated with the cylinder, it is advantageous to have the combustion duct extend approximately over half the piston and/or cylinder circumference.
The combustion duct associated with the cylinder can be overriden (overtraveled) in a simple manner by a piston part fashioned with an excessive height, which covers the combustion duct containing the source of ignition except for the end zone located away from the source of ignition. This end zone of the combustion duct terminates at a piston zone located at a lower level which, in a top view on the piston, can be fashioned as a crescent-shaped indentation.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.